In the processing of vinyl halide resins and more particularly polyvinyl chloride resins (hereafter PVC) to form moldable or extrudable compositions, it is customary to incorporate into the polymeric resin, generally in dry powder form, a variety of additives for special purposes and to achieve the desired properties in the molded or extruded products. Among the additives generally employed are internal and external lubricants, pigments, heat and light stabilizers, fillers, antioxidants and the like. While the stabilizers generally employed are the liquid organotin compounds and while they can be added in liquid form, the other additives are for the most part powders or granules. The normally solid additives can be added individually or as mixtures of such powders or granules and incorporated into the resinous polymeric powder in a mixer, typically a high shear mixer, in which the mechanical working of the material causes a rise in the temperature thereof and the additives become molten at temperatures of 100.degree. C. or higher and dispersed at the elevated temperature. For the most part, the normally liquid stabilizer is added to the polymer first and dispersed throughout the polymer at a relatively low temperature. Thereafter, the solid lubricants and waxes are generally added. Normally the lubricants generally include at least one wax that has a sufficiently low melting point to be melted in the mixer and become distributed on the surface of the polymeric powder. Then other additives may generally be added.
It has been recognized that such methodology is subject to a number of disadvantages and drawbacks. For example, numerous separate, time-consuming and error-prone weighings for each additive is required. Moreover, when masterbatching of additives is attempted, the difference in physical properties of the various additives has led to inhomogeneity of mixtures thereof. Additionally, such mixtures tend to produce non-uniform agglomerations initially, on storage or when introduced into the mixing apparatus with the polymeric powder. Since some additives are used at low levels of about 0.1 part per hundred parts of resin, phr, this becomes a serious problem.
In attempts to avoid such problems it has been suggested to mix the solid paraffinic hydrocarbon wax, employed as the external lubricant, with the other solid additives, heat the mixture to an elevated temperature of 100.degree. C. or higher and thereafter cooling to recover a solid glass-like friable composition to be added to the polymer. However, this process still leads to an undesirable solid which has to be mixed with the polymeric powder along with all the problems that entails. Another less than satisfactory suggestion has been to form an aqueous emulsion of lubricants and stabilizers which is then mixed with solid additive to form a free-flowing additive concentrate powder. However, this process also results in an undesirable solid powder to be added to the polymeric powder. Also attempts to add the additives in a molten state at elevated temperatures has been suggested but this has not really solved any of the problems.
Recently issued U.S. Pat. No. 4,719,022 of Jeffrey R. Hyde, assigned to Morton International, Inc., discloses that it is possible to incorporate all such additives as a liquid formulation which is liquid at normal ambient room temperature or a temperature of 50.degree. C. or less and thereby substantially avoid or eliminate the problems associated with the mixing of solid additives to resin powders. According to said patent these advantages are obtained by employing in sufficient quantity certain oils essentially derived from petroleum and which are liquid at normal ambient room temperature or at a temperature of about 50.degree. C. or less as substantially the only necessary external lubricant for rigid vinyl halide resin compositions. The oils derived essentially from petroleum which are employed according to said patent are aromatic, naphthenic, paraffinic, extracted naphthenic and extracted paraffinic oils which are liquids at ambient room temperature and meet the molecular weight/percent paraffin content criteria described hereinafter. The oils, in addition to being essentially derived from petroleum and being liquids at ambient room temperature, must be within a specified criteria based on the molecular weight and percent paraffin content of the oils. That is, the oils must have a molecular weight and percent paraffin content sufficient to satisfy the following formula: EQU (molecular weight).times.(% paraffin content).times.(10.sup.-4).gtoreq.2.0.
The viscosity of such oils which meet the hereinbefore described criteria can range, for example, from about 50 to about 8000 SSU at 100.degree. F. More preferably, the oils are those having a viscosity of from about 100 to about 750 SSU at 100.degree. F., and even more preferably are those oils having a viscosity of at least 300 SSU at 100.degree. F. Most preferably is an oil having a viscosity of about 575 SSU or more at 100.degree. F.
In general, the lower the viscosity and the lower the molecular weight/percent paraffin content criteria value of the oil employed the greater the amount of oil that must be employed in order for the oil to function as substantially the only necessary external lubricant additive in vinyl halide resin compositions. For example, oils having a viscosity of from about 100 to about 300 SSU are employed in an amount of from about 2% to about 3% or more by weight based upon the weight of the resin, with the amount required being generally inversely proportional to the viscosity of the oil. That is, an oil having a viscosity of about 100 SSU is employed in an amount of about 3% or more whereas an oil having a viscosity of about 300 SSU can be employed in an amount down to about 2% or more by weight. Oils having a viscosity of greater than 300 SSU need only be employed in an amount of from about 2% or less, generally down to about 0.5% by weight. That is, an oil having a viscosity of about 575 SSU need only be employed in an amount of about 0.5% to about 2.0% by weight, preferably about 1.4% by weight. Again the amount of oil required is generally inversely proportional to the viscosity of the oil, with the heavier viscosity oils requiring smaller minimum amounts than oils of lesser viscosity.
Such liquid aromatic as well as straight-run and extracted paraffinic and naphthenic oils that may be used according to said patent are generally available commercially. Especially preferred is an extracted paraffinic oil having a viscosity of about 575 SSU at 100.degree. F. and a molecular weight/paraffin content providing a value of about 3.57 according to the aforesaid criteria formula.
Along with said oils the patent discloses that one or more other processing and formulation additives for vinyl halide resins, such as liquid heat stabilizers and metal salt internal lubricants and stabilizers as well as metal release, fusion regulators, melt viscosity control agents and the like can also be employed and that the resulting lubricating and stabilizing compositions resulting are liquids at normal ambient room temperature or at temperature of about 50.degree. C. or less.
The oils of said patent can be combined with liquid vinyl halide heat stabilizers such as liquid organotin or antimony heat stabilizers generally known in the art, especially organotin mercapto carboxylic acid esters and organotin carboxylic acid mercapto alcohol esters such as those disclosed in U.S. Pat. Nos. 2,735,325; 2,641,596; 2,648,650, 4,062,881 and 4,701,486.
Examples of metal salt internal lubricants and stabilizers that may be employed in the liquid lubricating and stabilizing compositions of the invention in U.S. Pat. No. 4,719,022 include calcium, magnesium, zinc, barium and strontium salts of acids selected from tall oil acid, rosin acid, unsaturated fatty acids, saturated neo fatty acids and naphthenic acids. As unsaturated fatty acids salts especially useful in that invention the patent mentions salts of oleic, linoleic, linolenic, erucic, ricinoleic and brassidic acids. Especially preferred are calcium salts, especially calcium tallate, calcium rosinate, calcium oleate, calcium naphthenate and calcium neodecanoate. It is understood that mixtures of one or more salts may also be employed. When added to the liquid lubricating and stabilizing compositions of that patent containing the liquid oil and liquid heat stabilizer the metal salts are generally employed in an amount of from abcut 0.15 to about 1.0 parts by weight of the resin.
Oxidized polyolefins may be employed in the compositions of the invention of U.S. Pat. No. 4,719,022 as processing additives. As examples of such oxidized polyolefins waxes there can be mentioned, for example, oxidized polyolefins of olefins containing from 2 to 8 carbon atoms and particularly oxidized polyethylenes such as AC-629A, available from Allied Corp. When employed in the liquid lubricating and stabilizing compositions of the invention the oxidized polyolefins are present in an amount of from about 0.0 to about 0.3 parts by weight, most preferably about 0.125 parts by weight.
It has now been discovered that liquid lubricating stabilizer (LLS) compositions of U.S. Pat. No. 4,719,022 comprising the certain oils derived from petroleum and the liquid vinyl halide heat stabilizers, such as the organotin or antimony heat stabilizers, are and remain liquids essentially free of precipitates. However, when the metal salt internal lubricants and stabilizers, such as the calcium salts are present in the LLS compositions, especially at levels above 0.25 parts by weight, these metal salts cause the LLS to form either a very viscous inhomogeneous mass or gel or solid at temperatures required to produce the compositions or over a period of time such as a few weeks or more and the metal salt precipitates out. The presence of oxidized polyolefin wax in the LLS compositions exacerbates these problems.
Although the patentee in U.S. Pat. No. 4,719,022 states that the metal salt can be formed in situ with an excess of free fatty acid to prevent gelation, this produces another problem. The addition of free acid, e.g. oleic acid, to the LLS formulation tends to reduce the external/internal lubricant efficiency, therefore, one must add additional metal salt to keep the necessary external/internal lubricant balance with the result that the LLS formulation solidifies and the metal salt precipitates even more quickly. Moreover, it has been discovered that the free acid, e.g. oleic acid, is also detrimental to organotin mercaptide stabilizers since the free acid reacts with the organotin mercaptide to form organotin carboxylates which are less efficient as heat stabilizers. Thus, with excess free acid present one must increase the amount of tin stabilizer present in the LLS formulation to obtain a given level of stabilization, resulting in increased costs for the lubricant stabilizer composition.
It is therefore an object of this present invention to provide LLS compositions containing metal salt internal lubricants and stabilizers in which the problem of gelation and/or solidification as well as metal salt precipitation is substantially eliminated or greatly inhibited. A further object of the present invention is to provide such improved LLS compositions containing metal salt internal lubricants and stabilizers which remain liquid, metal salt precipitation is inhibited and the viscosity of the composition is favorably and significantly reduced without adversely affecting the rheological properties, particularly the external/internal lubricant balance, and stability of the rigid PVC formulations compounded using the LLS compositions.